ABSTRACT This project is a feasibility, acceptability, and pilot study that leverages the psychosocial benefits of informed and attached dog ownership among treatment-nave overweight or obese adolescents. We draw upon a socioecological model of health behavior that pursues multiple levels of influence, including those extending across species lines such as physical activity. We utilize BodyWorks, a Comprehensive Behavioral Family Lifestyle Interventions (CBFLI), a national, empirically validated, curriculum-based 7-week program offered at Children's Hospital Los Angeles AltaMed Division of General Pediatrics, a Federally Qualified Healthcare Center. The aims of the study are: Specific Aim 1: Using current empirical evidence in veterinary medicine, to develop a Canine Health Literacy module (CHL) to be delivered as part of the existing, empirically tested BW curriculum to increase adolescents' health literacy about their dogs' physical activity needs, weight status, and nutrition. Specific Aim 2: Test the feasibility and acceptability of a concurrent approach using physical activity trackers and Ecological Momentary Assessment. 2(a): Test the feasibility and acceptability of objective measurement of physical activity using wireless fitness trackers for adolescents (FitBit Ace), their parents (FitBit Flex2), and their dogs (FitBark); 2(b): Test the feasibility and acceptability of using mobile phones for Ecological Momentary Assessment of types and contexts of adolescent's physical activity with dogs. Specific Aim 3: To establish the size of the effect, and the variability associated with the 7 week-long BW + CHL module, as compared with the control group who received the standard BW program in 3(a) adolescents' positive affect during or after physical activity with the dog, as measured by the Ecological Momentary Assessment using prompts on mobile phones; and 3(b) levels of overall physical activity for the adolescents, their parents, and the dogs as measured by the FitBit Ace (adolescents), FitBit Flex2 (parents), and FitBark (dogs). The project will establish feasibility, acceptability, attrition, and protocol compliance, and will collect pilot data needed for power calculations in preparation for an R01 Randomized Controlled Trial as a next step to test the effectiveness of our enhanced BW+CHL program. This project represents a significant methodological and theoretical advancement in the field of Human-Animal Interaction (HAI) and in research on overweight and obesity.